These experiments propose to deal specifically with the question of chemical mediation in one resorption stimulated by the application of force. Pilot data have supported the hypothesis that chemical factors in the local microenvironment of bones exposed to forces can stimulate increased release of calcium from fetal bones. It will be determined if this stimulation calcium release is also reflected by an incrase in osteoclast numbers. If this correlation can be made, calcium release will be used as a bioassay for bone resorption in further studies of this phenomenon. Other major objectives will include a description of the effect of duration and degree of force application on the stimulation of such bone resorption mediator(s). Preliminary investigations will also be made into the chemical nature of this/these mediators(s). Correlations between the degree of root resorption in the test animals and amount of calcium release in the bioassay will also be made. Using simple orthodontic appliances on rats, tipping forces of known magnitude will be applied. The tissue immediately surrounding the point of pressure application and similar areas from control animals will be excised, homogenized and cleared of cellular debris. After normalizing these homogenates for wet weight of sample, their ability to stimulate resorptive activity will be assessed by bioassay. The bone resorption bioassay to be used is based on the release of pre-incorporated 45Ca from the fetal long bones into a tissue culture medium which has been treated with a test homogenate. The specific objectives will be carried out by generating and testing homogenates from alveolar bone exposed to forces for differing periods of time and of differing magnitudes. The chemical nature of this/these bone resorption mediator(s) will be investigated by perturbing the test homogenates and assessing alterations in their activities using the bioassy. The degree of root resorption will be assessed by quantitative SEM procedures.